As if the fact that Pokémon Global Link was postponed wasn't bad enough...
Most of the Wi-Fi features, including GTS and Wi-Fi Train, are down! The only Wi-Fi related thing that works is Wi-Fi Club and Random Matchup. (I don't actually know... I just got to the point where it said Free Mode or Rating Mode, and then I quit because I didn't actually want to use Random Matchup.)
It's not just me: someone has reported this on GameFAQs and Yahoo. Those are the only places, however.
The error code is 13724.
Speaking of error codes, the Error Codes page should be updated with the Gen IV and V Wi-Fi error codes.